Traditionally, inorganic materials have dominated the semiconductor industry. For example, silicon arsenide and gallium arsenide have been used as semiconductor materials, silicon dioxide has been used as an insulator material, and metals such as aluminum and copper have been used as electrode materials. In recent years, however, there has been an increasing research effort aimed at using organic materials rather than the traditional inorganic materials in semiconductor devices. Among other benefits, the use of organic materials may enable lower cost manufacturing of electronic devices, may enable large area applications, and may enable the use of flexible circuit supports for display backplanes or integrated circuits.
A variety of organic semiconductor materials have been considered, the most common being fused aromatic ring compounds as exemplified by tetracene and pentacene, bis(acenyl)acetylene, and acene-thiophenes; oligomeric materials containing thiophene or fluorene units; and polymeric materials such as regioregular poly(3-alkylthiophene). At least some of these organic semiconductor materials have performance characteristics such as charge-carrier mobility, on/off current ratios, and sub-threshold voltages that are comparable or superior to those of amorphous silicon-based devices.
Thiophene chemistry and the chemical stability of the thiophene ring hold potential for use of thiophene materials in molecular-based electronics and photonics. In particular, α,α′-conjugated thiophene oligomers (nTs) and polymers (polythiophenes-PTs) have attracted great interest as semiconducting elements in organic thin-film transistors (TFTs). To be useful in such devices and related structures, the organic material must support a channel of holes or electrons (p- or n-type semiconductor, respectively) created by the gate electrode bias, which switches the device “on”. Furthermore, the charge mobility of the material must be sufficiently large to increase the source-drain on-conduction by many orders of magnitude over the “off” state. The density of the charge carrier in the channel is modulated by voltage applied at the gate electrode
U.S. Pat. No. 6,585,914 (Marks et al.) describe α,ω-diperfluoroalkylsexithiophene-evaporated films of which behave as n-type semiconductors, and can be used to fabricate thin film transistors with FET mobilities about 0.01 cm2/Vs.